<!DOCTYPE html>
<html>
    <head lang="en">
        <meta charset="UTF-8">
        <title></title>
    </head>
    <body>
        <input type="checkbox" indeterminate id="cb">属性测试
        <script>
        var cb=document.getElementById("cb");
        cb.indeterminate=true;
        </script>
    </body>
</html>